Moulded bodies consisting of core-shell particles

ABSTRACT

The invention relates to moulded bodies having an effect, essentially consisting of core-shell particles comprising a shell which forms a matrix and a core which is essentially solid and has an essentially monodisperse size distribution, the refractive index of the core material being different from that of the shell material. The invention is characterized in that at least one contrast material is stored in the matrix.

The invention relates to mouldings having an optical effect whichessentially consist of core/shell particles, and to processes for theproduction of the mouldings.

Polymeric core/shell particles have been recommended for the productionof adhesives, binder systems, in particular also as reinforcingmaterials in the production of certain groups of composite materials.Composite materials of this type consist of a plastic matrix andreinforcing elements embedded therein. One problem in the production ofmaterials of this type consists in the production of a positiveconnection between the matrix material and reinforcing material. Only ifsuch a connection exists can forces be transferred from the matrix tothe reinforcing elements. The more the mechanical properties of thematrix material and reinforcing material, the elasticity, hardness anddeformability, differ from one another, the greater the risk ofdetachment of the matrix from the reinforcing elements. This risk iscountered by coating the polymeric reinforcing particles with a secondpolymer material which is more similar to the matrix material and istherefore able to form a stronger bond to the matrix (Young-Sam Kim,“Synthesis and Characterisation of Multiphase Polymeric Lattices Havinga Core/Shell Morphology”, dissertation, University of Karlsruhe (TH),Shaker Verlag, Aachen (1993), pages 2-22). In addition, it has also beenrecommended to graft the coating polymer onto the reinforcing polymer inorder also to prevent detachment of the shell from the reinforcingparticles by means of covalent bonds (W.-M. Billig-Peters, “Core/ShellPolymers with the Aid of Polymeric Azo Initiators”, dissertation,University of Bayreuth (1991).

The specific production of core/shell polymers is generally carried outby stepwise emulsion polymerisation, in which firstly a latex of coreparticles is produced in the first step, and the shell polymer isproduced in the second step, where the core particles act as “seedparticles” onto the surface of which the shell polymers preferablydeposit.

The deposition can grow onto the core particles to give a more or lesssymmetrical shell, but it is also possible for irregular depositions totake place, giving structures having a blackberry-like appearance. Agood review of the production of two-phase polymer particles and thephenomena which occur in the process, in particular the formation ofcore/shell particles, is given in the dissertation by KatharinaLandfester, “Synthesis and Characterisation of Core/Shell Lattices UsingElectron Microscopy and Solid-State NMR”, University of Mainz (1995).

Natural precious opals consist of monodisperse, regularly arrangedsilica gel spheres having diameters of 150-400 nm. The colour play ofthese opals is created by Bragg-like scattering of the incident light atthe lattice planes of the spheres arranged in a crystal-like manner.

There has been no lack of attempts to synthesise white and black opalsfor jewellery purposes using water-glass or silicone esters as startingmaterial.

U.S. Pat. No. 4,703,020 describes a process for the production of adecorative material consisting of amorphous silica spheres which arearranged in a three-dimensional manner, with zirconium oxide orzirconium hydroxide being located in the interspaces between thespheres. The spheres have a diameter of 150-400 nm. The production iscarried out in two steps. In a first step, silicon dioxide spheres areallowed to sediment from an aqueous suspension. The resultant materialis then dried in air and subsequently calcined at 800° C. In a secondstep, the calcined material is introduced into the solution of azirconium alkoxide, the alkoxide penetrating into the interspacesbetween the cores, and zirconium oxide being precipitated by hydrolysis.This material is subsequently calcined at 1000-1300° C.

A multiplicity of publications on the production of monodisperseparticles is known, for example EP-A-0 639 590 (production byprecipitation polymerisation), A. Rudin, J. Polym. Sci., 33 (1995)1849-1857 (monodisperse particles having a core/shell structure) andEP-A-0 292 261 (production with addition of seed particles).

EP-A-0 441 559 describes core/shell polymers having different refractiveindices the layers and their use as additives for paper-coatingcompositions.

EP-A-0 955 323 describes core/shell particles whose core and shellmaterials are able to form a two-phase system and which arecharacterised in that the shell material is filmable and the cores areessentially dimensionally stable under the conditions of film formationof the shell, are only swellable by the shell material to a very smallextent, or not at all, and have a monodisperse size distribution, with adifference between the refractive indices of the core material and shellmaterial of at least 0.001. The production of the core/shell particlesand their use for the production of effect colorants are also described.The process for the production of an effect colorant comprises thefollowing steps:

Application of the core/shell particles to a substrate of low adhesivecapacity, if necessary evaporation or expulsion of any solvent ordiluent present in the applied layer, transfer of the shell material ofthe core/shell particles into a liquid, soft or visco-elastic matrixphase, orientation of the cores of the core/shell particles at least toform domains having a regular structure, curing of the shell material inorder to fix the regular core structure, detachment of the cured filmfrom the substrate, and, if a pigment or powder is to be produced,comminution of the detached film to the desired particle size. In thesecore/shell particles disclosed in EP-A-0 955 323, the core “floats” inthe shell matrix; a long-range order of the cores does not form in themelt, merely a close-range order of the cores in domains. Theseparticles are thus of only restricted suitability for processing by theusual methods for polymers.

The earlier German patent application DE 10145450.3 discloses mouldingshaving an optical effect which essentially consist of core/shellparticles whose shell forms a matrix and whose core is essentially solidand has an essentially monodisperse size distribution. The refractiveindices of the core material and shell material differ here, producingthe said optical effect, preferably opalescence.

For decorative applications, it is desirable also to be able to producelarge-area structures or three-dimensional mouldings directly with along-range order of the cores which exhibit the optical effecthomogeneously over the entire area and with high brightness. Inparticular, it has been shown that materials having increased colourintensity of the observed effects are desired.

The object of the present invention was to avoid the above-mentioneddisadvantages and in particular to provide mouldings which exhibitcolour effects which are perceived as intense by the observer.

Surprisingly, it has now been found that it is possible to achieveintense effects of this type if contrast materials are introduced intothe “synthetic opal structures”.

A first subject-matter of the present invention are therefore mouldingshaving an optical effect, essentially consisting of core/shell particleswhose shell forms a matrix and whose core is essentially solid and hasan essentially monodisperse size distribution, where a difference existsbetween the refractive indices of the core material and shell material,which are characterised in that at least one contrast material has beenincorporated into the matrix.

The incorporated contrast materials effect an increase in brightness,contrast and depth of the observed colour effects in the mouldingsaccording to the invention. For the purposes of the invention, the termcontrast materials is taken to mean all materials which cause astrengthening of this type in the optical effect. The contrast materialsare usually pigments.

For the purposes of the present invention, the term pigments here istaken to mean any solid substance which exhibits an optical effect inthe visible wavelength region of light. In accordance with theinvention, the term pigments is applied here, in particular, tosubstances which conform to the definition of pigments in accordancewith DIN 55943 or DIN 55945. According to this definition, a pigment isan inorganic or organic, coloured or non-coloured colorant which isvirtually insoluble in the application medium. Both inorganic andorganic pigments can be employed in accordance with the invention.

Pigments can be divided into absorption pigments and lustre pigments inaccordance with their physical mode of functioning. Absorption pigmentsare pigments which absorb at least part of visible light and thereforecause a colour impression and in the extreme case appear black.According to DIN 55943 or DIN 55944, lustre pigments are pigments inwhich lustre effects arise through directed reflection at metallic orstrongly light-refracting pigment particles which are formed and alignedin a predominantly two-dimensional manner. These standards defineinterference pigments as lustre pigments whose colouring action is basedentirely or predominantly on the phenomenon of interference. Inparticular, these are so-called mother-of-pearl pigments orfire-coloured metal bronzes. Of economic importance amongst theinterference pigments are also, in particular, the pearlescent pigments,which consist of colourless, transparent and highly light-refractingplatelets. Depending on the orientation in a matrix, they produce a softlustre effect which is known as pearlescence. Examples of pearlescentpigments are guanine-containing pearl essence, pigments based on leadcarbonates, bismuth oxide chloride or titanium dioxide mica. Inparticular, the titanium dioxide micas, which are distinguished bymechanical, chemical and thermal stability, are frequently employed fordecorative purposes.

In accordance with the invention, it is possible to employ bothabsorption and lustre pigments, it also being possible, in particular,to employ interference pigments. It has been found that the use ofabsorption pigments is preferred, in particular for increasing theintensity of the optical effects. Both white and coloured or blackpigments can be employed here, where the term coloured pigments isintended to mean all pigments which give a colour impression other thanwhite or black, such as, for example, Heliogen™ Blue K 6850 (BASF, Cuphthalocyanine pigment), Heliogen™ Green K 8730 (BASF, Cu phthalocyaninepigment), Bayferrox™ 105 M (Bayer, iron oxide-based red pigment) orChromium Oxide Green GN-M (Bayer, chromium oxide-based green pigment).Owing to the colour effects achieved, preference is in turn givenamongst the absorption pigments to black pigments. For example, mentionmay be made here of pigment carbon black (for example the carbon blackproduct line from Degussa (in particular Purex™ LS 35 and Corax™ N 115))and iron oxide black, manganese black as well as cobalt black andantimony black. Black mica grades can also advantageously be employed asblack pigment (for example Iriodin™ 600, Merck; iron oxide-coated mica).

It has been found that it is advantageous in accordance with theinvention if the particle size of the at least one contrast material isat least twice as large as the particle size of the core material. Ifthe particles of the contrast material are smaller, only inadequateoptical effects are achieved. It is assumed that smaller particlesinterfere with the arrangement of the cores in the matrix and cause achange in the lattice which forms. The particles preferably employed inaccordance with the invention, which have a size which is at least twicethat of the cores, only interact locally with the lattice formed fromthe cores. Electron photomicrographs (see also Example 3) confirm thatthe incorporated particles only interfere with the lattice of coreparticles to a small extent, or not at all. The term particle size ofthe contrast materials, which are frequently also platelet-shaped aspigments, is in each case taken to mean here the largest dimension ofthe particles. If platelet-shaped pigments have a thickness in theregion of the particle size of the cores or even below, the presentstudies show that this does not interfere with the lattice orders. Ithas also been found that the shape of the incorporated contrast materialparticles has little or no influence on the optical effect. Bothspherical and platelet-shaped and needle-shaped contrast materials canbe incorporated in accordance with the invention. The only factor ofsignificance appears to be the absolute particle size in relation to theparticle size of the cores. It is therefore preferred for the purposesof the invention if the particle size of the at least one contrastmaterial is at least twice as large as the particle size of the corematerial, where the particle size of the at least one contrast materialis preferably at least four times as large as the particle size of thecore material, since the observable interactions are then even smaller.

A sensible upper limit for the particle size of the contrast materialsarises from the limit at which the individual particles themselvesbecome visible or impair the mechanical properties of the moulding owingto their particle size. Determination of this upper limits causes theperson skilled in the art, no difficulties at all.

Also of importance for the effect desired in accordance with theinvention is the amount of contrast material employed. It has been foundthat effects are usually observed if at least 0.05% by weight ofcontrast material, based on the weight of the moulding, are employed. Itis particularly preferred for the moulding to comprise at least 0.2% byweight and especially preferably at least 1% by weight of contrastmaterial since these increased contents of contrast material generallyalso result, in accordance with the invention, in more intense effects.

Conversely, relatively large amounts of contrast material under certaincircumstances adversely affect the processing properties of thecore/shell particles and thus make the production of mouldings accordingto the invention more difficult. In addition, it is expected that theformation of the lattice of core particles will be interfered with abovea certain proportion of contrast material, which is dependent on theparticular material, and instead oriented contrast material layers willform. It is therefore preferred in accordance with the invention for themoulding to comprise a maximum of 20% by weight of contrast material,based on the weight of the moulding, it being particularly preferred forthe moulding to comprise a maximum of 12% by weight and especiallypreferably a maximum of 5% by weight of contrast material.

In a particular embodiment of the present invention, however, it mayalso be preferred for the mouldings to comprise the largest possibleamounts of contrast material. This is the case, in particular, if thecontrast material is at the same time intended to increase themechanical strength of the moulding.

The mouldings according to the invention can be obtained essentiallyanalogously to the process described in the earlier German patentapplication DE 10145450.3, with a mixture of the core/shell particleswith at least one contrast material being employed instead of thecore/shell particles.

Consequently, the present invention furthermore relates to a process forthe production of mouldings having an optical effect, which ischaracterised in that core/shell particles whose shell forms a matrixand whose core is essentially solid and has an essentially monodispersesize distribution, where a difference exists between the refractiveindices of the core material and shell material, are mixed with at leastone contrast material.

The mixture is preferably subjected to a mechanical force at atemperature at which the shell is flowable.

In a preferred variant of the production of mouldings according to theinvention, the temperature at which the mixture is subjected to themechanical force is at least 40° C., preferably at least 60° C., abovethe glass transition temperature of the shell of the core/shellparticles. It has been found empirically that the flowability of theshell in this temperature range meets the requirements for economicalproduction of the mouldings to a particular extent.

In a likewise preferred process variant which results in the mouldingsaccording to the invention, the flowable mixtures are cooled under theaction of the mechanical force to a temperature at which the shell is nolonger flowable.

For the purposes of the present invention, the action of mechanicalforce can be the action of a force which occurs in the conventionalprocessing steps of polymers. In preferred variants of the presentinvention, the action of mechanical force takes place either:

-   -   through uniaxial pressing or    -   action of force during an injection-moulding operation or    -   during a transfer moulding operation,    -   during (co)extrusion or    -   during a calendering operation or    -   during a blowing operation.

If the action of force takes place through uniaxial pressing, themouldings according to the invention are preferably films. Filmsaccording to the invention can preferably also be produced bycalendering, film blowing or flat-film extrusion. The various ways ofprocessing polymers under the action of mechanical forces are well knownto the person skilled in the art and are revealed, for example, by thestandard textbook Adolf Franck, “Kunststoff-Kompendium” [PlasticsCompendium]; Vogel-Verlag; 1996.

If mouldings are produced by injection moulding, it is particularlypreferred for the demoulding not to take place until after the mouldwith moulding inside has cooled. When carried out in industry, it isadvantageous to employ moulds having a large cooling-channel crosssection since the cooling can then take place in a relatively shorttime. It has been found that cooling in the mould makes the coloureffects according to the invention much more intense. It is assumed thatbetter disordering of the core/shell particles to form the latticeoccurs in this uniform cooling operation. It is particularlyadvantageous here for the mould to have been heated before the injectionoperation.

In a preferred variant of the process according to the invention, astructured surface is simultaneously produced during the action ofmechanical force. This is achieved by the tools used already having asurface structuring of this type. For example, injection moulding can becarried out using corresponding moulds whose surface produces thisstructuring or uniaxial pressing can also be carried out usingcompression moulds in which at least one of the compression moulds has asurface structuring. For example, imitation leather which has aleather-like surface structure and at the same time exhibits the coloureffects discussed above can be produced using these methods.

The mouldings according to the invention may, if it is technicallyadvantageous, comprise auxiliaries and additives here. They can servefor optimum setting of the applicational data or properties desired ornecessary for application and processing. Examples of auxiliaries and/oradditives of this type are plasticisers, film-formation auxiliaries,flow-control agents, fillers, melting assistants, adhesives, releaseagents, application auxiliaries and viscosity modifiers, for examplethickeners.

Particularly recommended are additions of film-formation auxiliaries andfilm modifiers based on compounds of the general formulaHO—C_(n)—H_(2n)—O—(C_(n)H_(2n)—O)_(m)H, in which n is a number from 2 to4, preferably 2 or 3, and m is a number from 0 to 500. The number n canvary within the chain, and the various chain members can be incorporatedin a random or blockwise distribution. Examples of auxiliaries of thistype are ethylene glycol, propylene glycol, di-, tri- and tetraethyleneglycol, di-, tri- and tetrapropylene glycol, polyethylene oxides,polypropylene oxide and ethylene oxide-propylene oxide copolymers havingmolecular weights of up to about 15,000 and a random or block-likedistribution of the ethylene oxide and propylene oxide units.

If desired, organic or inorganic solvents, dispersion media or diluents,which, for example, extend the open time of the formulation, i.e. thetime available for its application to substrates, waxes or hot-meltadhesives are also possible as additives.

If desired, UV and weathering stabilisers can also be added to themouldings. Suitable for this purpose are, for example, derivatives of2,4-dihydroxybenzophenone, derivatives of 2-cyano-3,3′-diphenylacrylate, derivatives of 2,2′,4,4′-tetrahydroxybenzophenone, derivativesof o-hydroxyphenylbenzotriazole, salicylic acid esters,o-hydroxyphenyls-triazines or sterically hindered amines. Thesesubstances may likewise be employed individually or in the form of amixture.

The total amount of auxiliaries and/or additives is up to 40% by weight,preferably up to 20% by weight, particularly preferably up to 5% byweight, of the weight of the mouldings. Accordingly, the mouldingsconsist of at least 60% by weight, preferably at least 80% by weight andparticularly preferably at least 95% by weight, of core/shell particles.

In order to achieve the optical or photonic effect according to theinvention, it is desirable for the core/shell particles to have a meanparticle diameter in the range from about 5 nm to about 2000 nm. It maybe particularly preferred here for the core/shell particles to have amean particle diameter in the range from about 5 to 20 nm, preferablyfrom 5 to 10 nm. In this case, the cores may be known as “quantum dots”;they exhibit the corresponding effects known from the literature. Inorder to achieve colour effects in the region of visible light, it isparticularly advantageous for the core/shell particles to have a meanparticle diameter in the region of about 40-500 nm. Particularpreference is given to the use of particles in the range 80-500 nm sincein particles in this size range, the reflections of various wavelengthsof visible light differ significantly from one another, and thus theopalescence which is particularly important for optical effects in thevisible region occurs to a particularly pronounced extent in a very widevariety of colours. However, it is also preferred in a variant of thepresent invention to employ multiples of this preferred particle size,which then result in reflections corresponding to the higher orders andthus in a broad colour play.

For the purposes of the invention, the term optical effect is taken tomean both effects in the visible wavelength region of light and, forexample, also effects in the UV or infrared region. It has recentlybecome customary to refer to effects of this type in general as photoniceffects. All these effects are optical effects for the purposes of thepresent invention, where, in a preferred embodiment, the effect isopalescence in the visible region. In the sense of a conventionaldefinition of the term, the mouldings according to the invention arephotonic crystals (cf. Nachrichten aus der Chemie; 49(9) September 2001;pp. 1018-1025).

It is particularly preferred in accordance with the invention for thecore of the core/shell particles to consist of a material which iseither not flowable or becomes flowable at a temperature above themelting point of the shell material. This can be achieved through theuse of polymeric materials having a correspondingly high glasstransition temperature (T_(g)), preferably crosslinked polymers, orthrough the use of inorganic core materials. The suitable materials indetail are described below.

A further crucial factor for the intensity of the observed effects isthe difference between the refractive indices of core and shell.Mouldings according to the invention preferably have a differencebetween the refractive indices of the core material and shell materialof at least 0.001, preferably at least 0.01 and particularly preferablyat least 0.1. If the mouldings according to the invention are intendedto exhibit industrially useful photonic effects, refractive indexdifferences of at least 1.5 are preferred.

In a particular embodiment of the invention, further nanoparticles areincluded in the matrix phase of the mouldings in addition to the coresof the core/shell particles. These particles are selected with respectto their particle size in such a way that they fit into the cavities ofthe sphere packing of the cores and thus cause only little change in thearrangement of the cores. Through specific selection of correspondingmaterials and/or the particle size, it is firstly possible to modify theoptical effects of the mouldings, for example to increase theirintensity. Secondly, it is possible through incorporation of suitable“quantum dots”, to functionalise the matrix correspondingly. Preferredmaterials are inorganic nanoparticles, in particular nanoparticles ofmetals or of II-VI or III-V semiconductors or of materials whichinfluence the magnetic properties of the materials. Examples ofpreferred nanoparticles are gold zinc sulfide, haematite or galliumnitride.

The precise mechanism which results in the uniform orientation of thecore/shell particles in the mouldings according to the invention washitherto unknown. However, it has been found that the action of force isessential for the formation of the far-reaching order. It is assumedthat the elasticity of the shell material under the processingconditions is crucial for the ordering process. The chain ends of theshell polymers generally attempt to adopt a coiled shape. If twoparticles come too close, the coils are compressed in accordance withthe model concept, and repellent forces arise. Since the shell-polymerchains of different particles also interact with one another, thepolymer chains are stretched in accordance with the model if twoparticles move away from one another. Due to the attempts by theshell-polymer chains to re-adopt a coiled shape, a force arises whichpulls the particles closer together again. In accordance with the modelconcept, the far-reaching order of the particles in the moulding iscaused by the interaction of these forces.

Particularly suitable core/shell particles for the production ofmouldings according to the invention have proven to be those whose shellis bonded to the core via an interlayer.

In a preferred embodiment, the shell of these core/shell particlesessentially consists of uncrosslinked organic polymers, which arepreferably grafted onto the core via an at least partially crosslinkedinterlayer.

The shell here can consist either of thermoplastic or elastomericpolymers. Since the shell essentially determines the material propertiesand processing conditions of the core/shell particles, the personskilled in the art will select the shell material in accordance with theusual considerations in polymer technology. In particular if movementsor stresses in a material are to result in optical effects, the use ofelastomers as shell material is preferred. In mouldings according to theinvention, the separations between the core/shell particles are changedby such movements. The wavelengths of the interacting light and theeffects to be observed change correspondingly.

The core can consist of a very wide variety of materials. The essentialfactor according to the invention is, as already stated, that arefractive-index difference to the shell exists and the core remainssolid under the processing conditions.

It is furthermore particularly preferred in a variant of the inventionfor the core to consist of an organic polymer, which is preferablycrosslinked.

In another, likewise preferred variant of the invention, the coreconsists of an inorganic material, preferably a metal or semimetal or ametal chalcogenide or metal pnictide. For the purposes of the presentinvention, chalcogenides are taken to mean compounds in which an elementfrom group 16 of the Periodic Table of the Elements is theelectronegative bonding partner; pnictides are taken to mean those inwhich an element from group 15 of the Periodic Table of the Elements isthe electronegative bonding partner.

Preferred cores consist of metal chalcogenides, preferably metal oxides,or metal pnictides, preferably nitrides or phosphides. Metals in thesense of these terms are all elements which can occur as electropositivepartner compared with the counterions, such as the classical metals ofthe subgroups, or the main-group metals from the first and second maingroups, but also all elements from the third main group, as well assilicon, germanium, tin, lead, phosphorus, arsenic, antimony andbismuth. The preferred metal chalcogenides and metal pnictides include,in particular, silicon dioxide, aluminium oxide, gallium nitride, boronnitride, aluminium nitride, silicon nitride and phosphorus nitride.

The starting materials employed for the production of the core/shellparticles according to the invention in a variant of the presentinvention are preferably monodisperse cores of silicon dioxide, whichcan be obtained, for example, by the process described in U.S. Pat. No.4,911,903. The cores here are produced by hydrolytic polycondensation oftetraalkoxysilanes in an aqueous-ammoniacal medium, where firstly a solof primary particles is produced, and the resultant SiO₂ particles aresubsequently converted into the desired particle size by continuous,controlled metered addition of tetraalkoxysilane. This process enablesthe production of monodisperse SiO₂ cores having mean particle diametersof between 0.05 and 10 μm with a standard deviation of 5%.

Also preferred as starting material are SiO₂ cores which have beencoated with (semi)metals or non-absorbent metal oxides, such as, forexample, TiO₂, ZrO₂, ZnO₂, SnO₂ or Al₂O₃. The production of SiO₂ corescoated with metal oxides is described in greater detail in, for example,U.S. Pat. No. 5,846,310, DE 198 42 134 and DE 199 29 109.

The starting material employed can also be monodisperse cores ofnon-absorbent metal oxides, such as TiO₂, ZrO₂, ZnO₂, SnO₂ or Al₂O₃, ormetal-oxide mixtures. Their production is described, for example, in EP0 644 914. Furthermore, the process of EP 0 216 278 for the productionof monodisperse SiO₂ cores can readily be applied to other oxides withthe same result. Tetraethoxysilane, tetrabutoxytitanium,tetrapropoxyzirconium or mixtures thereof are added in one portion, withvigorous mixing, to a mixture of alcohol, water and ammonia, whosetemperature is set precisely to from 30 to 40° C. using a thermostat,and the resultant mixture is stirred vigorously for a further 20seconds, giving a suspension of monodisperse cores in the nanometreregion. After a post-reaction time of from 1 to 2 hours, the cores areseparated off in a conventional manner, for example by centrifugation,washed and dried.

Suitable starting materials for the production of the core/shellparticles according to the invention are furthermore also monodispersecores of polymers which contain included particles, for example metaloxides. Materials of this type are available, for example, from microcaps Entwicklungs-und Vertriebs GmbH in Rostock. Microencapsulationsbased on polyesters, polyamides and natural and modified carbohydratesare produced in accordance with customer-specific requirements.

It is furthermore possible to employ monodisperse cores of metal oxideswhich have been coated with organic materials, for example silanes. Themonodisperse cores are dispersed in alcohols and modified withconventional organoalkoxysilanes. The silanisation of spherical oxideparticles is also described in DE 43 16 814.

The cores of the core/shell particles according to the invention may, inaddition, also comprise dyes, for example so-called nanocolorants, asdescribed, for example, in WO 99/40123. The disclosure content of WO99/40123 is hereby expressly included in the disclosure content of thepresent application.

For the intended use of the core/shell particles according to theinvention for the production of mouldings, it is important that theshell material is filmable, i.e. that it can be softened,visco-elastically plasticised or liquefied by simple measures to such anextent that the cores of the core/shell particles are at least able toform domains having a regular arrangement. The regularly arranged coresin the matrix formed by film formation of the shell of the core/shellparticles form a diffraction grating, which causes interferencephenomena and thus results in very interesting colour effects. Thematerials of core and shell may, as long as they satisfy the conditionsindicated above, be of an inorganic, organic or even metallic characteror they may be hybrid materials.

In view of the possibility of varying the invention-relevant propertiesof the cores of the core/shell particles according to the invention asneeded, however, it is advantageous for the cores to comprise one ormore polymers and/or copolymers (core polymers) or to consist ofpolymers of this type.

The cores preferably comprise a single polymer or copolymer. For thesame reason, it is advantageous for the shell of the core/shellparticles according to the invention likewise to comprise one or morepolymers and/or copolymers (shell polymers; matrix polymers) or polymerprecursors and, if desired, auxiliaries and additives, where thecomposition of the shells may be selected in such a way that it isessentially dimensionally stable and tack-free in a non-swellingenvironment at room temperature.

With the use of polymer substances as shell material and, if desired,core material, the person skilled in the art gains the freedom todetermine their relevant properties, such as, for example, theircomposition, the particle size, the mechanical data, the refractiveindex, the glass transition temperature, the melting point and thecore:shell weight ratio and thus also the applicational properties ofthe core/shell particles, which ultimately also affect the properties ofthe mouldings produced therefrom.

Polymers and/or copolymers which may be present in the core material orof which it consists are high-molecular-weight compounds which conformto the specification given above for the core material. Both polymersand copolymers of polymerisable unsaturated monomers and polycondensatesand copolycondensates of monomers containing at least two reactivegroups, such as, for example, high-molecular-weight aliphatic,aliphatic/aromatic or fully aromatic polyesters, polyamides,polycarbonates, polyureas and polyurethanes, but also amino and phenolicresins, such as, for example, melamine-formaldehyde, urea-formaldehydeand phenolformaldehyde condensates, are suitable.

For the production of epoxy resins, which are likewise suitable as corematerial, epoxide prepolymers, which are obtained, for example, byreaction of bisphenol A or other bisphenols, resorcinol, hydroquinone,hexanediol or other aromatic or aliphatic diols or polyols, orphenolformaldehyde condensates, or mixtures thereof with one another,with epichlorohydrin or other di- or polyepoxides, are usually mixedwith further condensation-capable compounds directly or in solution andallowed to cure.

The polymers of the core material are advantageously, in a preferredvariant of the invention, crosslinked (co)polymers, since these usuallyonly exhibit their glass transition at high temperatures. Thesecrosslinked polymers may either already have been crosslinked during thepolymerisation or polycondensation or copolymerisation orcopolycondensation or may have been post-crosslinked in a separateprocess step after the actual (co)polymerisation or(co)polycondensation.

A detailed description of the chemical composition of suitable polymersfollows below.

In principle, polymers of the classes already mentioned above, if theyare selected or constructed in such a way that they conform to thespecification given above for the shell polymers, are suitable for theshell material and for the core material.

For certain applications, such as, for example, for the production ofcoatings or coloured films, it is favourable, as already stated above,for the polymer material of the matrix phase-forming shell of thecore/shell particles according to the invention to be an elasticallydeformable polymer, for example a polymer having a low glass transitiontemperature. In this case, it is possible to achieve a situation inwhich the colour of the moulding according to the invention varies onelongation and compression. Also of interest for the application arecore/shell particles according to the invention which, on filmformation, result in mouldings which exhibit dichroism.

Polymers which meet the specifications for a shell material are likewisepresent in the groups of polymers and copolymers of polymerisableunsaturated monomers and polycondensates and copolycondensates ofmonomers containing at least two reactive groups, such as, for example,high-molecular-weight aliphatic, aliphatic/aromatic or fully aromaticpolyesters and polyamides.

Taking into account the above conditions for the properties of the shellpolymers (=matrix polymers), selected units from all groups of organicfilm formers are in principle suitable for their production.

Some further examples are intended to illustrate the broad range ofpolymers which are suitable for the production of the shells.

If the shell is intended to have a comparatively low refractive index,polymers such as polyethylene, polypropylene, polyethylene oxide,polyacrylates, polymethacrylates, polybutadiene, polymethylmethacrylate, polytetrafluoroethylene, polyoxymethylene, polyesters,polyamides, polyepoxides, polyurethane, rubber, polyacrylonitrile andpolyisoprene, for example, are suitable.

If the shell is intended to have a comparatively high refractive index,polymers having a preferably aromatic basic structure, such aspolystyrene, polystyrene copolymers, such as, for example, SAN,aromatic-aliphatic polyesters and polyamides, aromatic polysulfones andpolyketones, polyvinyl chloride, polyvinylidene chloride and, onsuitable selection of a high-refractive-index core material, alsopolyacrylonitrile or polyurethane, for example, are suitable for theshell.

In an embodiment of core/shell particles which is particularly preferredin accordance with the invention, the core consists of crosslinkedpolystyrene and the shell of a polyacrylate, preferably polyethylacrylate and/or polymethyl methacrylate.

With respect to particle size, particle-size distribution andrefractive-index differences, the above-stated regarding the mouldingsapplies analogously to the core/shell particles according to theinvention.

With respect to the processability of the core/shell particles intomouldings, it is advantageous for the core:shell weight ratio to be inthe range from 2:1 to 1:5, preferably in the range from 3:2 to 1:3 andparticularly preferably in the region from 1:1 to 2:3. In general, it isadvantageous to increase the shell proportion if the particle diameterof the cores increases.

The core/shell particles to be employed in accordance with the inventioncan be produced by various processes. A preferred way of obtaining theparticles is a process for the production of core/shell particles by a)surface treatment of monodisperse cores, and b) application of the shellof organic polymers to the treated cores.

In a process variant, the monodisperse cores are obtained in step a1) byemulsion polymerisation.

In a preferred variant of the invention, a crosslinked polymericinterlayer, which preferably contains reactive centres to which theshell can be covalently bonded, is applied to the cores in step a),preferably by emulsion polymerisation or by ATR polymerisation. ATRpolymerisation here stands for atom transfer radical polymerisation, asdescribed, for example, in K. Matjaszewski, Practical Atom TransferRadical Polymerisation, Polym. Mater. Sci. Eng. 2001, 84. Theencapsulation of inorganic materials by means of ATRP is described, forexample, in T. Werne, T. E. Patten, Atom Transfer Radical Polymerisationfrom Nanoparticles: A Tool for the Preparation of Well-Defined HybridNaNO₃ structures and for Understanding the Chemistry ofControlled/“Living” Radical Polymerisation from Surfaces, J. Am. Chem.Soc. 2001, 123, 7497-7505 and WO 00/11043. The performance both of thismethod and of emulsion polymerisations is familiar to the person skilledin the art of polymer preparation and is described, for example, in theabove-mentioned literature references.

The liquid reaction medium in which the polymerisations orcopolymerisations can be carried out consists of the solvents,dispersion media or diluents usually employed in polymerisations, inparticular in emulsion polymerisation processes. The choice here is madein such a way that the emulsifiers employed for homogenisation of thecore particles and shell precursors are able to develop adequateefficacy. Suitable liquid reaction media for carrying out the processaccording to the invention are aqueous media, in particular water.

Suitable for initiation of the polymerisation are, for example,polymerisation initiators which decompose either thermally orphotochemically, form free radicals and thus initiate thepolymerisation. Preferred thermally activatable polymerisationinitiators here are those which decompose at between 20 and 180° C., inparticular at between 20 and 80° C. Particularly preferredpolymerisation initiators are peroxides, such as dibenzoyl peroxide,di-tertbutyl peroxide, peresters, percarbonates, perketals,hydroperoxides, but also inorganic peroxides, such as H₂O₂, salts ofperoxosulfuric acid and peroxodisulfuric acid, azo compounds, alkylboroncompounds, and hydrocarbons which decompose homolytically. Theinitiators and/or photoinitiators, which, depending on the requirementsof the polymerised material, are employed in amounts of between 0.01 and15% by weight, based on the polymerisable components, can be usedindividually or, in order to utilise advantageous synergistic effects,in combination with one another. In addition, use is made of redoxsystems, such as, for example, salts of peroxodisulfuric acid andperoxosulfuric acid in combination with low-valency sulfur compounds,particularly ammonium peroxodisulfate in combination with sodiumdithionite.

Corresponding processes have also been described for the production ofpolycondensation products. Thus, it is possible for the startingmaterials for the production of polycondensation products to bedispersed in inert liquids and condensed, preferably with removal oflow-molecular-weight reaction products, such as water or—for example onuse of di(lower alkyl) dicarboxylates for the preparation of polyestersor polyamides—lower alkanols.

Polyaddition products are obtained analogously by reaction of compoundswhich contain at least two, preferably three, reactive groups, such as,for example, epoxide, cyanate, isocyanate or isothiocyanate groups, withcompounds carrying complementary reactive groups. Thus, isocyanatesreact, for example, with alcohols to give urethanes, with amines to giveurea derivatives, while epoxides react with these complementary groupsto give hydroxyethers or hydroxyamines. Like the polycondensations,polyaddition reactions can also advantageously be carried out in aninert solvent or dispersion medium.

It is also possible for aromatic, aliphatic or mixed aromatic/aliphaticpolymers, for example polyesters, polyurethanes, polyamides, polyureas,polyepoxides or also solution polymers, to be dispersed or emulsified(secondary dispersion) in a dispersion medium, such as, for example, inwater, alcohols, tetrahydrofuran or hydrocarbons, and to bepost-condensed, crosslinked and cured in this fine distribution.

The stable dispersions required for these polymerisation,polycondensation or polyaddition processes are generally produced usingdispersion auxiliaries.

The dispersion auxiliaries used are preferably water-soluble,high-molecular-weight organic compounds having polar groups, such aspolyvinylpyrrolidone, copolymers of vinyl propionate or acetate andvinylpyrrolidone, partially saponified copolymers of an acrylate andacrylonitrile, polyvinyl alcohols having different residual acetatecontents, cellulose ethers, gelatine, block copolymers, modified starch,low-molecular-weight polymers containing carboxyl and/or sulfonylgroups, or mixtures of these substances.

Particularly preferred protective colloids are polyvinyl alcohols havinga residual acetate content of less than 35 mol %, in particular from 5to 39 mol %, and/or vinylpyrrolidone-vinyl propionate copolymers havinga vinyl ester content of less than 35% by weight, in particular from 5to 30% by weight.

It is possible to use nonionic or ionic emulsifiers, if desired also asa mixture. Preferred emulsifiers are optionally ethoxylated orpropoxylated, relatively long-chain alkanols or alkylphenols havingdifferent degrees of ethoxylation or propoxylation (for example adductswith from 0 to 50 mol of alkylene oxide) or neutralised, sulfated,sulfonated or phosphated derivatives thereof. Neutraliseddialkylsulfosuccinic acid esters or alkyldiphenyl oxide disulfonates arealso particularly suitable.

Particularly advantageous are combinations of these emulsifiers with theabove-mentioned protective colloids, since particularly finely divideddispersions are obtained therewith.

Special processes for the production of monodisperse polymer particleshave also already been described in the literature (for example R. C.Backus, R. C. Williams, J. Appl. Physics 19, p. 1186 (1948)) and canadvantageously be employed, in particular, for the production of thecores. It need merely be ensured here that the above-mentioned particlesizes are observed. A further aim is the greatest possible uniformity ofthe polymers. The particle size in particular can be set via the choiceof suitable emulsifiers and/or protective colloids or correspondingamounts of these compounds.

Through the setting of the reaction conditions, such as temperature,pressure, reaction duration and use of suitable catalyst systems, whichinfluence the degree of polymerisation in a known manner, and the choiceof the monomers employed for their production—in terms of type andproportion—the desired property combinations of the requisite polymerscan be set specifically.

Monomers which result in polymers having a high refractive index aregenerally those which contain aromatic moieties or those which containheteroatoms having a high atomic number, such as, for example, thosehalogen atoms, in particular bromine or iodine atoms, sulfur or metalions, i.e. atoms or atomic groups which increase the polarisability ofthe polymers.

Polymers having a low refractive index are accordingly obtained frommonomers or monomer mixtures which do not contain the said moietiesand/or atoms of high atomic number or only do so in a small proportion.

A review of the refractive indices of various common homopolymers isgiven, for example, in Ullmanns Encyklopädie der technischen Chemie[Ullmann's Encyclopaedia of Industrial Chemistry], 5th Edition, VolumeA21, page 169. Examples of monomers which can be polymerised by means offree radicals and result in polymers having a high refractive index are:

Group a): styrene, styrenes which are alkyl-substituted on the phenylring, α-methylstyrene, mono- and dichlorostyrene, vinylnaphthalene,isopropenylnaphthalene, isopropenylbiphenyl, vinylpyridine,isopropenylpyridine, vinylcarbazole, vinylanthracene,N-benzylmethacrylamide and p-hydroxymethacrylanilide.

Group b): acrylates containing aromatic side chains, such as, forexample, phenyl(meth)acrylate (=abbreviated notation for the twocompounds phenyl acrylate and phenyl methacrylate), phenyl vinyl ether,benzyl(meth)acrylate, benzyl vinyl ether, and compounds of the formulae:

In order to improve clarity and simplify the notation of carbon chainsin the formulae above and below, only the bonds between the carbon atomsare shown. This notation corresponds to the depiction of aromatic cycliccompounds, where, for example, benzene is depicted by a hexagon withalternating single and double bonds.

Also suitable are compounds containing sulfur bridges instead of oxygenbridges, such as, for example:

In the above formulae, R is hydrogen or methyl. The phenyl rings inthese monomers may carry further substituents. Such substituents aresuitable for modifying the properties of the polymers produced fromthese monomers within certain limits. They can therefore be used in atargeted manner to optimise, in particular, the applicationally relevantproperties of the mouldings according to the invention.

Suitable substituents are, in particular, halogen, NO₂, alkyl havingfrom one to twenty carbon atoms, preferably methyl, alkoxy having fromone to twenty carbon atoms, carboxyalkyl having from one to twentycarbon atoms, carbonylalkyl having from one to twenty carbon atoms or—OCOO— alkyl having from one to twenty carbon atoms. The alkyl chains inthese radicals may themselves optionally be substituted or interruptedby divalent heteroatoms or groups, such as, for example, —O—, —S—, —NH—,—COO—, —OCO— or —OCOO—, in non-adjacent positions.

Group c): monomers containing heteroatoms, such as, for example, vinylchloride, acrylonitrile, methacrylonitrile, acrylic acid, methacrylicacid, acrylamide and methacrylamide, or organometallic compounds, suchas, for example,

Group d): an increase in the refractive index of the polymers is alsoachieved by copolymerisation of carboxyl-containing monomers andconversion of the resultant “acidic” polymers into the correspondingsalts with metals of relatively high atomic weight, such as, forexample, preferably with K, Ca, Sr, Ba, Zn, Pb, Fe, Ni, Co, Cr, Cu, Mn,Sn or Cd.

The above-mentioned monomers, which make a considerable contributiontowards the refractive index of the polymers produced therefrom, can behomopolymerised or copolymerised with one another. They can also becopolymerised with a certain proportion of monomers which make a lessercontribution towards the refractive index. Such copolymerisable monomershaving a lower refractive index contribution are, for example,acrylates, methacrylates, or vinyl ethers or vinyl esters containingpurely aliphatic radicals.

In addition, crosslinking agents which can be employed for theproduction of crosslinked polymer cores from polymers produced by meansof free radicals are also all bifunctional or polyfunctional compoundswhich are copolymerisable with the above-mentioned monomers or which cansubsequently react with the polymers with crosslinking.

Examples of suitable crosslinking agents are presented below, dividedinto groups for systematisation:

Group 1: bisacrylates, bismethacrylates and bisvinyl ethers of aromaticor aliphatic di- or polyhydroxyl compounds, in particular of butanediol(butanediol di(meth)acrylate, butanediol bisvinyl ether), hexanediol(hexanediol di(meth)acrylate, hexanediol bisvinyl ether),pentaerythritol, hydroquinone, bishydroxyphenylmethane, bishydroxyphenylether, bishydroxymethylbenzene, bisphenol A or with ethylene oxidespacers, propylene oxide spacers or mixed ethylene oxide/propylene oxidespacers.

Further crosslinking agents from this group are, for example, di- orpolyvinyl compounds, such as divinylbenzene, or methylenebisacrylamide,triallyl cyanurate, divinylethyleneurea, trimethylolpropanetri(meth)acrylate, trimethylolpropane trivinyl ether, pentaerythritoltetra(meth)acrylate, pentaerythritol tetravinyl ether, and crosslinkingagents having two or more different reactive ends, such as, for example,(meth)allyl(meth)acrylates of the formulae:

in which R is hydrogen or methyl.

Group 2: reactive crosslinking agents which act in a crosslinkingmanner, but in most cases in a post-crosslinking manner, for exampleduring warming or drying, and which are copolymerised into the core orshell polymers as copolymers.

Examples thereof are: N-methylol(meth)acrylamide, acrylamidoglycolicacid, and ethers and/or esters thereof with C₁- to C₆-alcohols,diacetoneacrylamide (DAAM), glycidyl methacrylate (GMA),methacryloyloxypropyltrimethoxysilane (MEMO), vinyltrimethoxysilane andm-isopropenylbenzyl isocyanate (TMI).

Group 3: carboxyl groups which have been incorporated into the polymerby copolymerisation of unsaturated carboxylic acids are crosslinked in abridge-like manner via polyvalent metal ions. The unsaturated carboxylicacids employed for this purpose are preferably acrylic acid, methacrylicacid, maleic anhydride, itaconic acid and fumaric acid. Suitable metalions are Mg, Ca, Sr, Ba, Zn, Pb, Fe, Ni, Co, Cr, Cu, Mn, Sn and Cd.Particular preference is given to Ca, Mg and Zn, Ti and Zr.

Group 4: post-crosslinked additives, which are taken to mean bis- orpolyfunctionalised additives which react irreversibly with the polymer(by addition or preferably condensation reactions) with formation of anetwork. Examples thereof are compounds which contain at least two ofthe following reactive groups per molecule: epoxide, aziridine,isocyanate, acid chloride, carbodiimide or carbonyl groups, furthermore,for example, 3,4-dihydroxyimidazolinone and derivatives thereof(®Fixapret products from BASF).

As already explained above, post-crosslinking agents containing reactivegroups, such as, for example, epoxide and isocyanate groups, requirecomplementary reactive groups in the polymer to be crosslinked. Thus,isocyanates react, for example, with alcohols to give urethanes, withamines to give urea derivatives, while epoxides react with thesecomplementary groups to give hydroxyethers and hydroxyaminesrespectively.

The term post-crosslinking is also taken to mean photochemical curing oroxidative or air- or moisture-induced curing of the systems.

The above-mentioned monomers and crosslinking agents can be combined and(co)polymerised with one another as desired and in a targeted manner insuch a way that an optionally crosslinked (co)polymer having the desiredrefractive index and the requisite stability criteria and mechanicalproperties is obtained.

It is also possible additionally to copolymerise further commonmonomers, for example acrylates, methacrylates, vinyl esters, butadiene,ethylene or styrene, in order, for example, to set the glass transitiontemperature or the mechanical properties of the core and/or shellpolymers as needed.

It is likewise preferred in accordance with the invention for theapplication of the shell of organic polymers to be carried out bygrafting, preferably by emulsion polymerisation or ATR polymerisation.The methods and monomers described above can be employed correspondinglyhere.

In particular on use of inorganic cores, it may also be preferred forthe core to be subjected to a pre-treatment which enables binding of theshell before the shell is polymerised on. This can usually consist inchemical functionalisation of the particle surface, as is known from theliterature for a very wide variety of inorganic materials. It mayparticularly preferably involve application to the surface of chemicalfunctions which, as active chain end, enable grafting-on of the shellpolymers. Examples which may be mentioned in particular here areterminal double bonds, epoxy functions and polycondensable groups. Thefunctionalisation of hydroxyl-carrying surfaces with polymers isdisclosed, for example, in EP-A-337 144. Further methods for themodification of particle surfaces are well known to the person skilledin the art and are described, for example, in various textbooks, such asUnger, K. K., Porous Silica, Elsevier Scientific Publishing Company(1979).

The mouldings according to the invention may themselves be plasticmouldings which are sold as end products. In another preferredembodiment of the present invention, the mouldings are films which aresuitable for coating surfaces. With the aid of these films, surfaces canbe provided with a decorative finish. Another area of application of thematerials according to the invention is in textiles. Films or mouldingsaccording to the invention can be integrated into clothing, inparticular sports clothing. For example, parts of sports shoes can bemanufactured from these materials. If the materials are used in areaswhich deform during movement, a further colour effect which iscorrelated with the stretching and compression of the material isobserved in addition to the angle-dependent colour effect. In a furtherpreferred embodiment of this invention, the mouldings are converted intopigments. The pigments obtainable in this way are particularly suitablefor use in paints, surface coatings, printing inks, plastics, ceramics,glasses and cosmetic formulations. For this purpose, they can also beemployed mixed with commercially available pigments, for exampleinorganic and organic absorption pigments, metal-effect pigments and LCPpigments. The particles according to the invention are furthermore alsosuitable for the production of pigment preparations and for theproduction of dry preparations, such as, for example, granules. Pigmentparticles of this type preferably have a platelet-shaped structure withan average particle size of 5 μm-5 mm.

The pigments can be produced, for example, by firstly producing a filmfrom the core/shell particles, which may optionally be cured. The filmcan subsequently be comminuted in a suitable manner by cutting orcrushing and, if desired, subsequent grinding to give pigments ofsuitable size. This operation can be carried out, for example, in acontinuous belt process.

The pigment according to the invention can then be used for thepigmentation of surface coatings, powder coatings, paints, printinginks, plastics and cosmetic formulations, such as, for example, oflipsticks, nail varnishes, cosmetic sticks, compact powders, make-ups,shampoos and loose powders and gels.

The concentration of the pigment in the application system to bepigmented is generally between 0.1 and 70% by weight, preferably between0.1 and 50% by weight and in particular between 1.0 and 20% by weight,based on the total solids content of the system. It is generallydependent on the specific application. Plastics usually comprise thepigment according to the invention in amounts of from 0.01 to 50% byweight, preferably from 0.01 to 25% by weight, in particular from 0.1 to7% by weight, based on the plastic composition. In the coatings area,the pigment mixture is employed in amounts of from 0.1 to 30% by weight,preferably from 1 to 10% by weight, based on the coating dispersion. Inthe pigmentation of binder systems, for example for paints and printinginks for gravure printing, offset printing or screen printing, or asprecursor for printing inks, for example in the form of highly pigmentedpastes, granules, pellets, etc., pigment mixtures with sphericalcolorants, such as, for example, TiO₂, carbon black, chromium oxide,iron oxide, and organic “coloured pigments”, have proven particularlysuitable. The pigment is generally incorporated into the printing ink inamounts of 2-35% by weight, preferably 5-25% by weight and in particular8-20% by weight. Offset printing inks can comprise the pigment inamounts of up to 40% by weight or more. The precursors for printinginks, for example in the form of granules, as pellets, briquettes, etc.,comprise up to 95% by weight of the pigment according to the inventionin addition to the binder and additives. The invention thus also relatesto formulations which comprise the pigment according to the invention.

The following examples are intended to explain the invention in greaterdetail without limiting it.

EXAMPLES

Abbreviations Used:

-   BDDA butane-1,4-diol diacrylate-   SDS dodecyl sulfate sodium salt-   SDTH sodium dithionite-   APS ammonium peroxodisulfate-   KOH potassium hydroxide-   ALMA allyl methacrylate-   MMA methyl methacrylate-   EA ethyl acrylate

Example 1 Production of Core/Shell Particles

A mixture, held at 4° C., consisting of 217 g of water, 0.4 g ofbutanediol diacrylate, 3.6 g of styrene (BASF, destabilised) and 80 mgof sodium dodecylsulfate (SDS; Merck) is introduced into a stirredreactor, pre-heated to 75° C., fitted with propeller stirrer, argonprotective-gas inlet and reflux condenser, and dispersed with vigorousstirring. Directly after the introduction, the reaction is initiated bydirect successive addition of 50 mg of sodium dithionite (Merck), 250 mgof ammonium peroxodisulfate (Merck) and a further 50 mg of sodiumdithionite (Merck), in each case dissolved in 5 g of water. After 10minutes, a monomer emulsion comprising 6.6 g of butanediol diacrylate,59.4 g of styrene (BASF, destabilised), 0.3 g of SDS, 0.1 g of KOH and90 g of water is metered in continuously over a period of 210 minutes.The reactor contents are stirred for 30 minutes without furtheraddition. A second monomer emulsion comprising 3 g of allylmethacrylate, 27 g of methyl methacrylate (BASF, destabilised), 0.15 gof SDS (Merck) and 40 g of water is subsequently metered in continuouslyover a period of 90 minutes. The reactor contents are subsequentlystirred for 30 minutes without further addition. A monomer emulsioncomprising 130 g of ethyl acrylate (BASF, destabilised), 139 g of waterand 0.33 g of SDS (Merck) is subsequently metered in continuously over aperiod of 180 minutes. The mixture is subsequently stirred for a further60 minutes for virtually complete reaction of the monomers. Thecore/shell particles are subsequently precipitated in 1 l of methanol, 1l of distilled water is added, and the particles are filtered off withsuction and dried.

Scanning and transmission electron photomicrographs of the core/shellparticles show that the particles have a particle size of 220 nm.

While carrying out the experiment analogously, the particles size of theparticles can be varied via the surfactant concentration in theinitially introduced mixture. Selection of corresponding amounts ofsurfactant gives the following particle sizes: Amount of surfactant [mgof SDS] Particle size [nm] 80 220 90 200 100 180 110 160

Example 2 Production of Granules of the Core/Shell Particles

3 kg of the core/shell particles from Example 1 are comminuted in thecutting mill (Rapid, model 1528) with ice cooling and subsequently mixedwith 2% by weight of black pigment (Iriodin®600 or Black Mica®; Merck)or with 0.2% by weight of a coloured absorption pigment (for examplePV-Echtblau A2R; Clariant) and suitable processing assistants (0.1% byweight of antioxidants, 0.2% by weight of UV stabilisers 0.2% by weightof mould-release agents and 0.2% by weight of flow improvers). After 15minutes in the drum mixer (Engelmann; model ELTE 650), the mixture iscompounded in a single-screw extruder (Plasti-Corder; Brabender; screwdiameter 19 mm with 1-hole die (3 mm)). After a cooling zone, theextrudate is granulated in an A 90-5 granulator (Automatik). 0.2% byweight of release agent are subsequently added to the granules in thedrum mixer over the course of 10 minutes.

Example 3a Production of a Film from Core/Shell Particles

2 g of the granules from Example 2 are heated to a temperature of 120°C. without pressure in a Collin 300P press and pressed at a pressure of30 bar to give a film. After cooling to room temperature, the pressureis reduced again.

Transmission electron photomicrographs (FIG. 1) show particles having asize of 180 nm and in each case a contrast material particle. It can beseen that the alignment of the cores in the shell matrix to give anextended crystal lattice is scarcely affected by the contrast material.

The optical analysis (visual or VIS reflection spectroscopy) confirmsthat core/shell particles having a size of 160 nm (FIG. 2) result infilms having a blue basic colour, core/shell particles having a size of180 nm result in films having a green basic colour (FIG. 3), andcore/shell particles having a size of 220 nm result in films having ared basic colour (FIG. 4). The spectra were measured using a PerkinElmer Lambda 900 UV/VIS/NIR spectrometer with optical bench. Thedirected reflection was recorded at various irradiation angles insingle-beam operation, and the spectra were standardised by means of asingle-channel spectrum. The spectra confirm the visual impression ofthe colour flop of the films.

Example 3b Production of a Film from Core/Shell Particles

25 g of the granules from Example 2 are heated to a temperature of 150°C. at a pressure of from 1 bar for 3 minutes between two polyethyleneterephthalate films in a press with cartridge cooling system (Dr. CollinGmbH; model 300E), subsequently pressed at a pressure of 250 bar and atemperature of 150° for 3 minutes, and cooled to room temperature undera pressure of 200 bar for 8 minutes. The polyethylene terephthalateprotective films are subsequently removed.

Example 4 Production of Mouldings by Injection Moulding

3 kg of the core/shell particles from Example 1 are comminuted in arapid mill with ice cooling and subsequently mixed with 120 g of pigment(Iriodin® 600) over the course of 30 minutes in a drum mixer(Engelmann). The resultant mixture is compounded in a Plasti-Corder(Brabender), comminuted in an ASG 5-1 granulator (Automatik), andprocessed further in a Klockner Ferromatik 75 FX 75-2Finjection-moulding machine, giving mouldings having an optical effect.

Example 5 Production of a Flat Film (Tape)

Granules from Example 2 are processed in a flat-film machine consistingof a single-screw extruder (Göttfert; model Extrusiometer; screwdiameter 20 mm; L/D 25), a thickness-adjustable film die (width 135 mm)and a heatable polishing stack (Leistritz; roll diameter 15 mm; rollwidth 350 mm). A film tape with a width of 125 mm and a thickness of 1mm is obtained.

Example 6 Production of Core/Shell Particles Having a Silicon DioxideCore (150 nm)

66 g of Monospher® 150 suspension (Merck; solids content 38% by weight,corresponding to 25 g of SiO₂ monospheres; average particle size 150 nm;standard deviation of the average particle size <5%) are introduced with354 g of water into a stirred twin-wall reactor, held at 25° C., fittedwith argon protective-gas inlet, reflux condenser and propeller stirrer,a solution of 450 mg of aluminium trichloride hexahydrate (Acros) in 50ml is added, and the mixture is stirred vigorously for 30 minutes. Asolution of 40 mg of sodium dodecylsulfate in 50 g of water issubsequently added, and the mixture is stirred vigorously for a further30 minutes.

50 mg of sodium dithionite, 150 mg of ammonium peroxodisulfate and afurther 50 mg of sodium dithionite, in each case in 5 g of water, arethen added directly one after the other. Immediately after the addition,the reactor is heated to 75° C., and 25 g of ethyl acrylate are meteredin continuously over a period of 120 minutes. The reactor contents aresubsequently stirred at 75° C. for a further 60 minutes for completereaction of the monomer.

The resultant hybrid material is filtered off and dried and convertedinto a film in accordance with Examples 2/3 or injection-moulded to givea moulding in accordance with Example 4.

Example 7 Production of Core/Shell Particles Having a Silicon DioxideCore (250 nm)

60 g of Monospher® 250 (Merck; average particle size 250 nm; standarddeviation of the average particle size <5%) are suspended. 3.2 g ofAlCl₃ and 1.9 g of Na₂SO₄ are added to the suspension. 5.9 g of3-methacryloxypropyltrimethoxysilane are added dropwise at pH=2.6 and75° C. At 75° C., a pH=8.5 is set by addition of, sodium hydroxidesolution. After hydrolysis, the resultant powder is separated off anddried.

90 g of water and 50 mg of sodium dodecylsulfate are added to 10 g ofthe functionalised Monospher® 250, and the mixture is stirred vigorouslyfor 1 day for dispersal. The suspension is subsequently dispersed in ahomogeniser (Niro Soavi, NS1001L). 70 g of water are added to thedispersion, and the mixture is cooled to 4° C.

The dispersion is subsequently introduced into a stirred twin-wallreactor fitted with argon protective-gas inlet, reflux condenser andpropeller stirrer. 50 mg of sodium dithionite, 150 mg of ammoniumperoxodisulfate and a further 50 mg of sodium dithionite, in each casein 5 g of water, are then added directly one after the other.Immediately after the addition, the reactor is heated to 75° C., and anemulsion of 10 g of ethyl acrylate and 20 g of water is metered incontinuously over a period of 120 minutes. The reactor contents aresubsequently stirred at 75° C. for a further 60 minutes for completereaction of the monomer.

The resultant hybrid material is precipitated in a solution of 10 g ofcalcium chloride and 500 g of water, filtered off and dried andconverted into a film in accordance with Examples 2/3 orinjection-moulded to give a moulding in accordance with Example 4.

Example 8 Production of Core/Shell Particles Having a Core Built Up fromSilicon Dioxide and an Outer Sheath of Titanium Dioxide

80 g of Monospher®100 (monodisperse silicon dioxide beads having a meansize of 100 nm with a standard deviation of <5%) from Merck KGaA aredispersed in 800 ml of ethanol at 40° C. A freshly prepared solutionconsisting of 50 g of tetraethyl orthotitanate (Merck KGaA) and 810 mlof ethanol is metered into the Monospher/ethanol dispersion togetherwith deionised water with vigorous stirring. The metering is initiallycarried out over a period of 5 minutes at a dropwise addition rate of0.03 ml/min (titanate solution) or 0.72 ml/min. The titanate solution isthen added at 0.7 ml/min and the water at 0.03 ml/min until thecorresponding containers are completely empty. For further processing,the ethanolic dispersion is stirred under reflux at 70° C. with cooling,and 2 g of methacryloxypropyltrimethoxysilane (ABCR), dissolved in 10 mlof ethanol, are added over a period of 15 minutes. After the mixture hasbeen refluxed overnight, the resultant powder is separated off anddried. 90 g of water and 50 mg of sodium dodecylsulfate are added to 10g of the functionalised silicon dioxide/titanium dioxide hybridparticles, and the mixture is stirred vigorously for 1 day fordispersal. The suspension is subsequently dispersed in a homogeniser(Niro Soavi, NS1001L). 70 g of water are added to the dispersion, andthe mixture is cooled to 4° C.

The dispersion is subsequently introduced into a stirred twin-wallreactor with argon protective-gas inlet, reflux condenser and propellerstirrer. 50 mg of sodium dithionite, 150 mg of ammonium peroxodisulfateand a further 50 mg of sodium dithionite, in each case in 5 g of water,are then added directly one after the other. Immediately after theaddition, the reactor is heated to 75° C., and an emulsion of 10 g ofethyl acrylate and 20 g of water is metered in continuously over aperiod of 120 minutes. The reactor contents are subsequently stirred at75° C. for a further 60 minutes for complete reaction of the monomer.

The resultant hybrid material is precipitated in a solution of 10 g ofcalcium chloride and 500 g of water, filtered off and dried andconverted into a film in accordance with Examples 2/3 orinjection-moulded to give a moulding in accordance with Example 4.

Example 9 Production of Core/Shell Particles Having a Core ofPolystyrene, a P(ALMA-co-MMA) Interlayer and a P(EA-co-MMA) Shell (20%of MMA)

A mixture, held at a temperature of 7° C., consisting of 1519 g ofdeionised water (aerated with N₂), 0.56 g of 1,4-butanediol diacrylate(BDDA) (MERCK), 25.2 g of styrene (MERCK), 1110 mg of sodiumdodecylsulfate (NaDS) (MERCK) and 350 mg of sodium dithionite (SDTH)(MERCK) is introduced into a 5-l jacketed reactor, held at a temperatureof 75° C., with double propeller stirrer, argon protective gas inlet andreflux condenser and dispersed with vigorous stirring. The reaction isthen initiated by successive injection of 1750 mg of ammoniumperoxodisulfate (APS) (MERCK) and 350 mg of SDTH, each dissolved in 10ml of deionised water. After 20 minutes, a monomer emulsion consistingof 56.7 g of BDDA (MERCK), 510.3 g of styrene (MERCK), 2.625 g of NaDS(MERCK), 0.7 g of potassium hydroxide (MERCK) and 770 g of deionisedwater (aerated with N₂) is continuously metered in via a rotary pistonpump over the course of 120 minutes. The reactor contents are thenstirred for a further 30 minutes.

450 mg of APS (MERCK) in 10 ml of deionised water are then injected,and, after a further 10 minutes, a second monomer emulsion consisting of10.5 g of allyl methacrylate (MERCK), 94.5 g of methyl methacrylate(MERCK), 0.525 g of NaDS and 140 g of deionised water (aerated with N₂)is then added continuously with stirring over a period of 30 minutes bymeans of a rotary piston pump.

After 45 minutes, a third monomer emulsion consisting of 760 g of ethylacrylate (MERCK), 2.613 g of NaDS, 190 g of methyl methacrylate (MERCK)and 950 g of deionised water (aerated with N₂) is metered incontinuously with stirring over a period of 240 minutes via a rotarypiston pump. The mixture is then stirred at 75° C. for a further 60minutes.

Residual monomers are removed by steam distillation. The materialobtained is precipitated in a solution of 10 g of calcium chloride and500 g of water, filtered off and dried and converted into a film inaccordance with Examples 2/3 or injection-moulded to give a moulding inaccordance with Example 4. The resultant mouldings are distinguished byreduced tack and at the same time reduced elasticity compared withmouldings produced from materials having a pure PEA shell (cf. Example1).

FIGURES

FIG. 1: Transmission electron photomicrograph of a plan view of a filmproduced in accordance with Examples 1 to 3 (particle size of thecore/shell particles: 180 nm; contrast material: 4% by weight ofIriodin™600). In addition to the ordered core/shell particles (dark-greydots), a particle of the contrast material Iriodin™600 can be seen.

FIG. 2: Reflection spectra of a film of core/shell particles with a sizeof 160 nm produced as described in Example 3. The spectra were measuredusing a Perkin Elmer Lambda 900 UV/VIS/NIR spectrometer with opticalbench. The directed reflection was recorded at various irradiationangles in single-beam operation, and the spectra were standardised bymeans of a single-channel spectrum. The spectra confirm the visualimpression of the colour flop of the films.

FIG. 3: Reflection spectra of a film of core/shell particles with a sizeof 180 nm produced as described in Example 3. The spectra were measuredusing a Perkin Elmer Lambda 900 UV/VIS/NIR spectrometer with opticalbench. The directed reflection was recorded at various irradiationangles in single-beam operation. The spectra confirm the visualimpression of the colour flop of the films.

FIG. 4: Reflection spectra of a film of core/shell particles with a sizeof 220 nm produced as described in Example 3. The spectra were measuredusing a Perkin Elmer Lambda 900 UV/VIS/NIR spectrometer with opticalbench. The directed reflection was recorded at various irradiationangles in single-beam operation. The spectra confirm the visualimpression of the colour flop of the films.

1. Moulding having an optical effect, essentially consisting ofcore/shell particles whose shell forms a matrix and whose core isessentially solid and has an essentially monodisperse size distribution,where a difference exists between the refractive indices of the corematerial and shell material, characterised in that at least one contrastmaterial has been incorporated into the matrix.
 2. Moulding according toclaim 1, characterised in that the moulding is obtainable by a processin which a mixture of core/shell particles with at least one contrastmaterial is subjected to the action of a mechanical force at atemperature at which the shell is flowable.
 3. Moulding according toclaim 1, characterised in that the core consists of a material which iseither not flowable or becomes flowable at a temperature above themelting point of the shell material.
 4. Moulding according to claim 1,characterised in that the moulding is obtainable by a process in whichthe temperature at which the mixture is subjected to the mechanicalforce is at least 40° C., preferably at least 60° C., above the glasstransition temperature of the shell.
 5. Moulding according to claim 2characterised in that the moulding is obtainable by a process in whichthe mixture is cooled to a temperature at which the shell is no longerflowable under the action of the mechanical force.
 6. Moulding accordingto claim 1, characterised in that the action of the mechanical force iscarried out by uniaxial pressing, and the moulding is preferably a film.7. Moulding according to claim 1, characterised in that the action ofthe mechanical force is carried out during an injection-mouldingoperation.
 8. Moulding according to claim 1, characterised in that theaction of the mechanical force is carried out during an extrusion. 9.Moulding according to claim 1, characterised in that the mouldingconsists of at least 60% by weight, preferably at least 80% by weightand particularly preferably at least 95% by weight of core/shellparticles.
 10. Moulding according to claim 1, characterised in that thecore/shell particles have a mean particle diameter in the range fromabout 5 nm to about 2000 nm, preferably in the range from about 5 to 20nm or in the range 40-500 nm.
 11. Moulding according to claim 1,characterised in that the difference between the refractive indices ofthe core material and shell material is at least 0.001, preferably atleast 0.01 and particularly preferably at least 0.1.
 12. Mouldingaccording to claim 1, characterised in that the at least one contrastmaterial is a pigment, preferably an absorption pigment and particularlypreferably a black pigment.
 13. Moulding according to claim 1,characterised in that the particle size of the at least one contrastmaterial is at least twice as large as the particle size of the corematerial, where the particle size of the at least one contrast materialis preferably at least four times as large as the particle size of thecore material.
 14. Moulding according to claim 1, characterised in thatthe moulding comprises at least 0.05% by weight of contrast material,based on the weight of the moulding, it being particularly preferred forthe moulding to comprise at least 0.2% by weight and especiallypreferably at least 1% by weight of contrast material.
 15. Mouldingaccording to claim 1, characterised in that the moulding comprises amaximum of 20% by weight of contrast material, based on the weight ofthe moulding, it being particularly preferred for the moulding tocomprise a maximum of 12% by weight and especially preferably a maximumof 5% by weight of contrast material.
 16. Moulding according to claim 1,characterised in that, in addition to the cores and the contrastmaterial, further nanoparticles, preferably inorganic nanoparticles,particularly preferably nanoparticles of metals, such as gold, or ofII-VI or III-V semiconductors, such as zinc sulfide or gallium arsenide,have been incorporated into the matrix phase.
 17. Process for theproduction of mouldings having an optical effect, characterised in thatcore/shell particles whose shell forms a matrix and whose core isessentially solid and has an essentially monodisperse size distribution,where a difference exists between the refractive indices of the corematerial and, shell material, are mixed with at least one contrastmaterial.
 18. Process for the production of mouldings according to claim17, characterised in that the mixture is subjected to a mechanical forceat a temperature at which the shell is flowable.
 19. Process for theproduction of mouldings according to claim 18, characterised in that, ina subsequent step, the mixture is cooled to a temperature at which theshell is no longer flowable under the action of the mechanical force.